PEM fuel cells (polymer electrolyte membrane fuel cells) are electrochemical cells consisting, simplified, of anode, cathode and interposed polymeric solid electrolytes. To operate such cells, fuels are continuously supplied externally to both electrodes, where they are electrochemically converted so that a voltage can be tapped on the electrodes. It is not possible, however, to convert the entire energy supplied. A certain part is always lost as heat in the operation of the fuel cell. Especially higher-output fuel cells require therefore measures for heat dissipation. According to the prior art, this is effected with the use of electrically conductive heat exchanger plates through which a coolant is passed (literature: A. J. Appley, E. B. Yeager, Energy 11, 137-152 1986!).
Both sides of the membrane-electrode unit are in contact with the electrically conductive plates, with interposed gaskets being used to achieve cell tightness. The conductive plates are configured as heat exchangers, that is, they contain ducts through which flows as coolant. The coolant is introduced and drained by way of openings contained in the plate. Integrated in the electrically conductive plates are also feed and drain ducts for the fuels, with the fuels then being supplied to the electrodes via suitable structures. For such fuel cell structure according to the prior art it is necessary, however, that the plates consist of electrically conductive material, since each plate must bear down on the respective eletrode area so as to establish the outward electrical connection of the cell. In the case of a stacked design, the plates may be fashioned also as bipolar plates.
To achieve higher outputs, and especially for achieving a higher voltage, it is known also to combine several membrane-electrode units, as described above, to a so-called fuel cell stack (U.S. Pat. No. 4,175,165 "Fuel cell system utilizing ion exchange membranes and bipolar plates"). To that end, a plurality of such cells, as described above, have so far been constructed separately, arranged successively and electrically wired in series, making the voltages of the individual cells additive. The design-related expense of such a series circuit is very high, however, since each membrane-electrode unit requires a separate fuel supply. This makes for a very high engineering expense for such cells.